I've had several of each one. Both are excellent. Something to consider is the grip-length in the pic of the five knives. Both the Dua and Beast have a grip-length which is in-between the lengths of the small and large Sebenza. I cannot hold onto a small (2nd from the top) in my hand. When I try to CLOSE the blade, I move my hand back a bit so that I can push on the lockbar with my thumb...at which time the small Sebenza falls out of my hand; too short a grip for my rather large hands. I have a pic of this at the bottom. So I carry a large Sebbie or Zaan, but both of these are larger/longer than I really need. I keep waiting for that "medium" Sebenza.
Jay S had this comment above:
"The flat part of the handle right before the blade is where the cutout for the pointer finger should be. Instead it places it back about an inch which screws up the balance and the amount of grip on the knife." This was my finding also. I asked Mike Grayman about this, and he said the cutout could not be placed any further forward...due to the position of the pivot. And that's too bad, because I really like this knife. It is a fat S30V, but you can re-profile. Note that this orange Dua has a grip-height which makes it sit better in my hand.
I've had two Dua's and three TSF's. The M390 that Jim Allen uses in his TSF is a great steel. Deployment is excellent and smooth and tight lockup.
This is my latest TSF Beast, with a re-profiled and sharpened/polished blade. It performed well in the "rubber-band" test that is in another thread this morning.

From top down: TSF Beast, small Sebbie, Seb 25 (ignore blood), DUA, Zaan.